Fluid-cooled carrier member of a composite electrode of an electric arc furnace

ABSTRACT

In a fluid-cooled clamp member (1) of a composite electrode (2) of an electric arc furnace, disposed in the flow path (13) for the coolant is a shut-off device (14) which is biassed in the closure direction, having an actuating member (15) by means of which the shut-off device (14) is put into the open condition in opposition to the biassing force, when a replaceable lower portion (2) of the composite electrode, which is subject to burning away, is screwed on. In the event of fracture of the lower portion in the region of the nipple (5), the flow path (13) is closed off by the actuating member (15) being released. The screwthreaded nipple is additionally protected by means of a protective cap which is screwed on to the screwthreaded nipple, the cap having an external screwthread corresponding to the internal screwthread of the lower portion (2).

The invention relates to a cylindrical clamp member of a compositeelectrode.

In the clamp member of that kind, which is disclosed in No.EP-B1-0010305, secured to the lower end is a screwthreaded portion or anipple, for screwing on a replaceable lower portion which is made ofgraphite and which is subject to burning off. The screwthreaded portionhas ducts for the coolant, the ducts being supplied with the coolant byway of the cooling system of the clamp member. In one embodiment of theknown mounting arrangement, the cooling system which carries theelectrode current and the cooling fluid includes an inner metal tubewhich is fitted into an outer metal tube at a spacing therefrom, theannular space defined between the two tubes communicating with theinterior of the inner metal tube in the lower region of the clampmember. The coolant, being generally water, is fed to the interior ofthe inner metal tube by way of connection, above the point at which theclamp member is gripped, flows downwardly into the region of thescrewthreaded portion and is there returned into the annular space whichis defined between the two metal tubes and which, above the point atwhich the clamp member is gripped in position in the crosshead, includesa further connection for the discharge of the cooling water. Disposedoutside the clamp member in the cooling water feed or in the coolingwater return is a device for measuring the amount of cooling waterwhich, when the rate of coolant through-put falls below a prescribedvalue, produces an alarm signal which can be used to pull the clampmember upwardly by way of the electrode control system.

When a composite electrode with a clamp member of the above-indicatedkind is used in an electric arc furnace in which scrap metal is beingmelted down, mechanical loadings can have the effect that thereplaceable lower portion fractures in the region of the screwthreadedportion or nipple and then the composite electrode is moved furtherdownwardly by the electrode control system, which generally results indamage to the lower tip of the clamp member, which is now no longerprotected, and possibly also results in the cooling fluid escaping.

The object of the present invention is to provide a clamp member with asignalling means which, in the event of fracture of the replaceablelower portion in the region of the screwthreaded portion or nipple,produces a signal which can be utilised for raising the clamp member. Inaddition, the invention seeks to provide that, in that case, the feedflow of coolant can be immediately interrupted in order to minimise theamount of coolant that escapes, in the event of damage to the lower tipof the clamp member.

The invention further seeks to provide that, in the event of fracture ofthe replaceable lower portion in the above-mentioned region, thescrewthreaded portion is protected from damage and thus the requiredmaintenance operations on the clamp member are substantially reduced.

In accordance with one aspect of the invention, in the clamp member ofthe composite electrode, disposed in the coolant flow path is a shut-offor closure means which is biassed in the closure direction, having anactuating member by means of which the shut-off means can be moved intothe opened condition against the biassing force when a replaceable lowerportion is screwed on to the screwthreaded portion. Thus, the flow pathis closed when the lower portion is removed and opened when the lowerportion is screwed on. If the lower portion is forcibly removed in theevent of electrode fracture at the location of the screwthreaded portionor nipple, then the biassing force of the shut-off means provides thatthe flow path is immediately closed off, in other words, the throughflowof coolant is abruptly interrupted and, when using an incompressiblecoolant such as water, that control operation has its effect immediatelyat any point in the flow path and can thus be utilised as an alarmsignal in respect of electrode fracture and a control signal for theelectrode control system. That means that there are no additional cablesor leads for an alarm system. Preferably, the shut-off means is disposedin the flow path of the feed to the lower tip of the clamp member and aflow meter for detecting the closed condition of the shut-off means isdisposed in the feed to the clamp member so that, in the event of damageto the unprotected tip after electrode rupture and coolant escape atthat point not only does the alarm system remain intact but in additionthe feed of coolant to the damaged location is interrupted. The shut-offor closure means therefore performs two functions, on the one hand beinga signal generator for the flow meter which is disposed in the coolantfeed and which in turn supplies a control signal to the electrodecontrol system, while on the other hand the shut-off means is a closuremember which cuts off the feed flow of coolant to the damaged part ofthe tip of the clamp member. In that way, the coolant which is containedin the flow path up to the shut-off member can be held back andprevented from being discharged into the furnace.

In accordance with another aspect of the invention, the screwthreadedportion or screwthreaded nipple on to which the lower portion of thecombination electrode is screwed is protected by a protective cap whichpreferably comprises graphite and which has an outside screwthread on towhich the lower portion of the electrode can be screwed. The protectivecap then forms an intermediate member which remains on the screwthreadednipple in the event of fracture of the lower portion of the electrode inthe region of the screwthreaded nipple, and protects the screwthreadednipple from damage by arcs. The damaged protective cap can be quicklyand easily replaced by unscrewing it from the screwthreaded nipple ofthe clamp member. The cap is an inexpensive element which, in the caseof screwthreaded nipples which are of a conical or taperedconfiguration, can also be screwed on to already existing fluid-cooledclamp members. Preferably, the two aspects of the invention as set forthabove are combined, that is to say, besides the protective cap, thearrangement also has the shut-off means described in this application.

The invention will now be described by means of three embodiments withreference to the eight figures of accompanying drawings in which:

FIG. 1 is a view in longitudinal section of part of a fluid-cooled clampmember with screwed-on lower portion of a composite electrode,

FIG. 2 is a view in section taken along line II--II in FIG. 1,

FIG. 3 is a view in cross-section taken along line III--III in FIG. 1,

FIG. 4 is a view of the screwthreaded portion of a fluid-cooled clampmember with protective cap screwed thereon, from below,

FIG. 5 is a view in longitudinal section of a part of the screwthreadedportion of the clamp member and the protective cap screwed thereon,

FIG. 6 is a view of the end, which bears against the screwthreadedportion, of the sleeve member shown in FIG. 5,

FIG. 7 is a view in longitudinal section of half of a protective cap,and

FIG. 8 is a view corresponding to that shown in FIG. 5, with anactuating member as shown in FIG. 1.

The fluid-cooled clamp member illustrated in FIG. 1, for a replaceablelower portion 2, which is liable to be burnt away, of a compositeelectrode of an electric arc furnace includes an exposed outer metaltube 3 whose upper portion is of approximately the same diameter as thelower portion 2 of the electrode and which can be gripped in position inan electrode crosshead of an electric arc furnace. At the end remotefrom the gripping location, that is to say, at its lower end, the metaltube 3 carries a flange 4 and a screwthreaded portion 5 for screwing onthe lower portion 2. The diameter of the lower portion of the metal tube3, which in the operating condition extends into the interior of thefurnace, is reduced in relation to the diameter of the lower portion 2.

Disposed at a spacing from the outer metal tube 3 is an inner metal tube6. The space or cavity 7 in the inner metal tube serves as a duct forthe feed flow of coolant, preferably cooling water, to the fluid-cooledscrewthreaded portion 5. The return flow of cooling water is by way ofthe space 8 defined between the outer and inner metal tubes. At theupper end of the fluid-cooled clamp member 1, the space 7 communicateswith a connection for the supply line (feed) and the space 8communicates with a connection for the return (return flow) of thecoolant.

The electrode current is introduced into the upper portion of the outermetal tube 3, and is carried downwardly in the metal tube 3 whichcomprises steel, and pases by way of the screwthreaded portion 5 whichcomprises electrolytic copper, into the lower portion 2 which is fittedon to the nipple.

A number of inner bores or holes 9 and a number of outer bores or holes10 are provided in the flange 4. The bores 9 are distributed in acircular array around the centre line of the clamp member 1 and areconnected to the space 7, while the bores 10 are also distributed in acircular array of larger diameter around the centre line and communicatewith the space 8. The bores serve as ducts for the feed and dischargeflow of coolant, to and from the duct 12 which is defined in thescrewthreaded portion 5 by an annular displacement member 11. The flowpath for the coolant is indicated by arrows 13.

In accordance with the invention, disposed in the flow path 13 is ashut-off means 14 which is biassed in the shut-off or closure direction,having an actuating member 15. When the lower portion 2 is screwed on tothe screwthreaded portion 5, the flow path 13 is opened by the actuatingmember 15 while when the lower portion 2 is removed, the flow path isclosed off. For that purpose, with the shut-off means 14 in the closedcondition, the actuating member 15 projects out of the screwthreadedportion 5, as indicated in FIG. 1 by the dash-dotted position shown at16, into a region which, when the lower portion is screwed on to thescrewthreaded portion, is occupied by a region of the lower portion. Theimportant consideration is that, when the lower portion 2 is screwed on,the actuating member 15 is actuated in opposition to the biassing forceof the shut-off means, by any region of the lower portion or a memberwhich is disposed on the lower portion, as a result of which the flowpath 13 is opened.

A preferred embodiment of the shut-off means will be described in detailhereinafter.

The actuating member 15 of the shut-off means 14 is in the form of a rodwhich is guided within a sleeve 17 which is fixed coaxially in theflange 4 and in the screwthreaded portion 5, being welded to thosecomponents in the illustrated embodiment. With the exception of thelower part, the sleeve 17 is disposed around the actuating member 15 ata spacing therefrom so that an annular duct 18 for the coolant is formedbetween the actuating member 15 and the sleeve 17. The duct 18communicates with the duct 12 by way of ducts 19. In that way, the flowpath 13 has a branched-off or diversion portion as indicated at 13a.Good cooling for the actuating member 15 can be achieved by way of thebranch portion 13a of the flow path. The actuating member 15 is guidedby the lower part of the sleeve 17 which has annular seals 20 in orderto prevent the coolant from escaping, and by a guide element 21 which isfitted into the sleeve 17 and which is of the form shown in FIG. 3.

At its upper end, the actuating member 15 carries a plate-like shut-offmember 22 which is welded thereonto. When the lower portion 2 isremoved, with the actuating member 15 occupying the position shown indash-dotted lines at 16, the shut-off member 22 assumes the positionwhich is also illustrated in dash-dotted lines and indicated at 23, inwhich it closes the inner bores 9 and the annular duct 18 of the sleeve17 and thus blocks the flow path 13. When the lower portion 2 isremoved, the shut-off member 22 is moved into the closure position by abiassing force which is produced on the one hand by the fluid pressurein the space 7 in the inner metal tube 6 and on the other hand by acompression spring 24 which bears against a holder 25. The holder 25,the configuration of which is shown in FIG. 2, is fixed in the lowerpart of the inner metal tube 6, being welded thereto in the illustratedembodiment, and carries a guide spigot or projection 26 for thecompression spring 24. The compression spring 24 bears against theplate-like shut-off member 22 where it is also guided by a spigot orprojection 27 which is screwed thereto. The lower end of the actuatingmember which, in the event of electrode fracture, is directly exposed tothe atmosphere in the furnace, is of an easily replaceable construction.In the present case, it comprises an end member 28 which is screwedthereon.

In the operative condition, the shut-off means occupies the positionshown in solid lines in FIG. 1. In the event of fracture of anelectrode, that is to say, fracture of the lower portion 2 whichpreferably comprises graphite, in the region of the nipple, theactuating member 15 is released and the plate-like shut-off member 22,together with the actuating member 15, is urged downwardly by the fluidpressure in the space 7 and by the force of the compression spring 24,whereby the feed flow to the inner bores 9 and to the annular duct 18 isabruptly interrupted. When the coolant is an incompressible coolant suchas water, that switching operation is registered virtually without anytime delay by a monitoring means in the coolant feed system, and acontrol signal is supplied to the electrode control system whichimmediately pulls the clamp member in question upwardly. If thescrewthreaded portion 5 should suffer damage as a consequence of thefracture of the electrode, the fluid in the space 7 is prevented fromescaping by the plate-like shut-off member 22.

Of the rod-like or bar-like, fluid-cooled clamp member withscrewthreaded nipple 101 for screwing on the replaceable lower portionof a composite electrode, FIG. 5 shows only the screwthreaded nipple101. In the illustrated embodiment, it comprises copper and, as in thecase of the first embodiment, is welded to the lower end of the clampmember which includes a metal cooling system for carrying the electrodecurrent. The screwthreaded nipple 101 has ducts (also not shown) for thecoolant, which are supplied with the coolant by way of the coolingsystem of the clamp member. The screwthreaded nipple is of a conical ortapered configuration in the usual fashion and is provided with anoutside screwthread corresponding to the inside screwthread of thereplaceable lower portion of the composite electrode.

A protective cap 102 of graphite or a refractory material is screwed onto the screwthreaded nipple 101. For that purpose, the protective cap102 has an inside screwthread corresponding to the outside screwthreadon the screwthreaded nipple 101, that is to say, it has a screwthreadwhich is identical to the inside screwthread of the lower portion whichotherwise is to be screwed on to the nipple 101. The screwthreadconnection is denoted by reference numeral 103.

In the same manner as the screwthreaded nipple 101, the protective cap102 is of a conical or tapered configuration and is provided at itsoutside peripheral surface with an outside screwthread 104 whichcorresponds to the inside screwthread in the lower portion of thecomposite electrode, which is to be screwed on to the protective cap102. A means as indicated at 105 is provided for preventing rotarymovement as between the protective cap 102 and the screwthreaded nipple101.

In the illustrated embodiment, the securing means 105 comprises twoeccentrically and diametrally disposed holes 106 which extend throughthe end portion of the protective cap 102 and two correspondinglyarranged screwthreaded holes 107 which are provided in the end face ofthe screwthreaded nipple 101 and into each of which a respective screw108 is screwed. The head of the screw 108 bears by way of a washer 109against a shoulder 110 in a sleeve member 111 which preferably comprisesrefractory material and whose outside diameter is adapted to thediameter of the hole 106. As FIGS. 4 and 6 show, the sleeve member 111has a slot 112 which is stepped in the axial direction of the sleevemember 111 and thus forms the shoulder 110. Tolerances in thescrewthread connection 103 can be compensated for, by means of the slot112. In order to improve the adhesion between the sleeve member 111 andthe end face of the screwthreaded nipple 101, the end face of the sleeve111 which bears against the face of the screwthreaded nipple 101 isprovided with grooves 113 (see FIG. 6). The sleeve member 111 and thescrew 108 are recessed in the end portion 116 of the protective cap 102and are thus protected in the event of electrode fracture. The spacebetween the recessed screw 108 and the outer end face 114 of theprotective cap 102 is filled with refractory ramming material 115. Inorder to enhance the resistance to fracture or rupture of the protectivecap 102, the outside screwthread 104 is turned off, in the region of theend portion 116 as far as the beginning of the inside screwthread, thatis to say, there is a screwthread-free portion 117. In the operatingcondition, the lower portion of the composite electrode is screwed on tothe outside screwthread 104 of the protective cap 102.

If the protective cap is damaged after an electrode fracture in theregion of the screwthreaded nipple, the damage protective cap 102 isreplaced by a fresh protective cap, in the following manner.

Firstly, the two screws 108 and the sleeve members 111 are removed andthe damaged protective cap is then unscrewed by means of a key which hastwo pegs fitting into the holes 106. A fresh protective cap 102 is thenscrewed on to the screwthreaded nipple 101 with the key. In thatposition, the screwthreaded bores 107 are in the region of the holes 106so that, after the sleeves 111 have been inserted, the screws 108 can bescrewed in, thus securing the protective cap against rotary movementwith respect to the screwthreaded nipple 101. After a fresh lowerportion of the composite electrode has been screwed on to the protectivecap 102, the fault has been rectified.

FIG. 7 shows a view in longitudinal section of half of theabove-described protective cap 102.

Preferably, the protective cap is provided in conjuction with theshut-off means described above with reference to FIGS. 1 through 3. Forthat purpose, the protective cap and possibly the shut-off means aremodified in such a way that the shut-off means can be moved into theopen condition when the lower portion of the electrode is screwed on tothe protective cap. FIG. 8 shows a corresponding arrangement. In thatconstruction, provided in a protective cap 102a is a bore 118 throughwhich is extended an end portion 28a which is screwed on to theactuating member 15a of the shut-off means 14 (see FIG. 1). In theillustrated closed position of the shut-off means, the end member 28aprojects beyond the bottom end face of the protective cap 102a. when thelower portion 2 (see FIG. 1) of the composite electrode is screwed on,the actuating member 15a is urged upwardly and opens the coolingcircuit. In the event of fracture of the lower portion in the region ofthe protective cap 102a, the nipple 101a is protected while in the eventof any damage to the protective cap 102 a and the end member 28a, thosecomponents can be easily and rapidly replaced.

We claim:
 1. A cylindrical clamp member (1) of a composite electrode,which clamp member can be fixed to the electrode crosshead of anelectric arc furnace and which includes a flow path (13) for a coolantand which at a lower end carries a screwthreaded portion (5) forscrewing on a replaceable lower portion (2) of the composite electrode,which lower portion is liable to being burnt away, characterized in thatdisposed in the flow path (13) is a shut-off means (14) which is biassedin the closure direction, having an actuating member (15) by which theshut-off means (14) can be put into the open condition against thebiassing force when the lower portion (2) is screwed on to thescrewthreaded portion (5).
 2. A clamp member as set forth in claim 1characterised in that the actuating member (15), in the closed conditionof the shut-off means (14), projects from the screwthreaded portion (5)in a region which is occupied by a region of the lower portion (2) whenthe lower portion is screwed on.
 3. A clamp member as set forth in claim2 characterised in that the shut-off means (14) includes an axiallydisplaceable rod as the actuating member (15), which rod at one endcarries a shut-off member (22) which is disposed in the flow path (13),and at the other end projects out of the end of the screwthreadedportion (5).
 4. A clamp member as set forth in claim 3 characterised inthat the actuating member (15) is guided within a sleeve (17) providedwith ducts (18, 19) for the coolant.
 5. A clamp member as set forth inclaim 1 characterised in that in a lower portion thereof, in the flowpath (13) for the coolant, it has a flange (4) through which passes atleast one duct (9), and the duct can be closed off by the shut-off means(14).
 6. A clamp member as set forth in claim 5 characterised in thatthe flange (4) has a plurality of ducts (9) which are closable by aplate-like shut-off member (22).
 7. A clamp member as set forth in claim1 characterised in that the shut-off means (14) is biassed by a spring(24).
 8. A clamp member as set forth in claim 1 characterised in thatthe shut-off means (14) is biassed by the pressure of the coolant.
 9. Aclamp member as set forth in claim 1 characterised in that thescrewthreaded portion (5) includes a duct (12) for the coolant, which isdisposed in the flow path (13) for said coolant.
 10. A clamp member asset forth in claim 5 characterised in that the sleeve member (17) iscoaxially fixed in a flange (4) and in the screwthreaded portion (5).11. A clamp member as set forth in claim 9, characterized in that itincludes further ducts (18, 19) in the screwthreaded portion, an innermetal tube (6) and at a spacing therefrom an outer metal tube (3), whichmetal tubes are closed off and connected in a lower portion thereof by aflange (4) which has ducts (9 and 10) communicating respectively with aspace (7) in the inner metal tube (6) and an intermediate space (8)between the two metal tubes (6 and 13), the last named ducts (9 and 10)communicating with the duct (12) for the coolant and the further ducts(18, 19) in the screwthreaded portion respectively, and that at theupper end the clamp member has a connection for the coolant, whichcommunicates with the space (7) in the inner metal tube (6), and aconnection which communicates with the space (8) between the two metaltubes (6 and 3).
 12. A clamp member as set forth in claim 1characterised in that there is provided a protective cap (102a) whichincludes an end portion which is screwed on to the screwthreaded portion(101a) and which has an outside screwthread (104) corresponding to theinside screwthread of the lower portion (2) to be screwed on, and arotation-preventing means (105) for preventing rotary movement asbetween the protective cap (102a) and the screwthreaded portion (101a),and that the shut-off means (14) can be put into the open condition whenthe lower portion (2) is screwed on to the protective cap (102a).
 13. Acylindrical clamp member (1) of a composite electrode, which clampmember can be fixed to the electrode crosshead of an electric arcfurnace and which includes a flow path (13) for a coolant and which at alower end carries a screwthreaded portion (5) for screwing on areplaceable lower portion (2) of the composite electrode, which lowerportion is liable to being burnt away, characterised by a protective cap(102) which includes an end portion which is screwed on to andsubstantially covers the screwthreaded portion (101) and which has anoutside screwthread (104) corresponding to the inside screw-thread ofthe lower portion to be screwed on, and a rotation-preventing means(105) for preventing rotary movement as between the protective cap (102)and the screwthreaded portion (101).
 14. A clamp member as set forth inclaim 12 characterised in that the outside of the protective cap (102)has a screwthread-free portion (117) in the region of an end portion(116) of the cap.
 15. A clamp member as set forth in claim 12characterised in that the screwthreaded portion (101) and the protectivecap (102) are of a tapered configuration.
 16. A clamp member as setforth in claim 12 characterised in that the protective cap (102) issecured against rotation by means of at least one screw (108) which isfitted at an eccentric position into an end of the screwthreaded portion(101) and which is countersunk in an end portion (116) of the protectivecap (102).
 17. A clamp member as set forth in claim 16 characterised inthat at least one eccentrically disposed through hole (106) is providedin the end portion (116) of the protective cap (102), wherein a sleevemember (111, 111') whose outside diameter is adapted to the diameter ofthe hole (106) and which has a slot (112) therein is fitted into saidhole (106) as an intermediate member between the head of the screw (108)and the end face of the screwthreaded portion (101).
 18. A clamp memberas set forth in claim 12 characterised in that the protective cap (102)comprises graphite.
 19. A clamp member as set forth in claim 13characterised in that the outside of the protective cap (102) has ascrewthread-free portion (117) in the region of an end portion (116) ofthe cap.
 20. A clamp member as set forth in claim 13 characterised inthat the screwthreaded portion (101) and the protective cap (102) are ofa tapered configuration.
 21. A clamp member as set forth in claim 13characterised in that the protective cap (102) is secured againstrotation by means of at least one screw (108) which is fitted at aneccentric position into an end of the screwthreaded portion (101) andwhich is countersunk in an end portion (116) of the protective cap(102).
 22. A clamp member as set forth in claim 21 characterised in thatat least one eccentrically disposed through hole (106) is provided inthe end portion (116) of the protective cap (102), wherein a sleevemember (111, 111') whose outside diameter is adapted to the diameter ofthe hole (106) and which has a slot (112) therein is fitted into saidhole (106) as an intermediate member between the head of the screw (108)and the end face of the screwthreaded portion (101).
 23. A clamp memberas set forth in claim 13 characterised in that the protective cap (102)comprises graphite.